schmitt trigger

A thermocouple circuit produces an amplified voltage difference of 0.5V when there is a change in temperature of 10°C.Thermocouple amplified voltage at 30°C is 2.5V.The thermocouple circuit is to be used as a temperature sensor to maintain an oven temperature between 40°C and 80°C by switching ON and OFF the power supply to the oven.The oven is to be controlled by schmitt trigger in connection with the thermocouple circuit.The schmitt trigger is to be connected to ±15V.
(a) Determine schmitt trigger voltage levels (upper and lower trigger level)
(b)Sketch hysteresis loop and show all necessary voltage levels
(c)draw the schmitttrigger circuit and determine reference voltage

It's not ok. If it is nonlinear, then knowing what the voltage is at 10C and 30C is not enough information for us to determine what it is at 40C and 80C.

It's also not ok since you haven't shown any effort to solve it yourself. Show what you have done thus far and where you are having problems and we will help guide you back to the right path. And, please, don't just say that you don't know were to start.